Problem: 4 glue sticks cost $5.00. Which equation would help determine the cost of 6 glue sticks?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 6 glue sticks. Since 6 glue sticks cost $x$ , we have the following proportion: $\dfrac{6}{x}$ We can write the fact that 4 glue sticks cost $5.00 as a proportion: $\dfrac{4}{\$5.00}$ The cost changes along with the number of glue sticks purchased, and so the two proportions are equivalent. $\dfrac{6}{x} = \dfrac{4}{\$5.00}$